Branched Siloxanes And Methods For Synthesis

ABSTRACT

The present invention describes branched and functionalized siloxanes and methods for making such compounds. The compounds have a variety of uses. One preferred application is as novel planarizing material for lithography, in which case functionalized branched siloxane, such as an epoxy-modified branched siloxane is particularly useful.

FIELD OF THE INVENTION

The present invention relates to branched siloxanes and methods forsynthesis of branched siloxanes, including, but not limited to,functionalized branched siloxanes. Such compounds have many usesincluding multiple applications in the semiconductor industry includingplanarizing layers, patternable insulators, and the like.

BACKGROUND OF THE INVENTION

Liquid branched siloxanes having low viscosity, low vapor pressure andhigh silicon content are useful for the semiconductor industry such asthe manufacturing of micro processors, flash memory, visual displaydevices and optical devices (light emitting diodes), etc. For example,Michael Lin et al. reported a UV curable liquid branched siloxane namedSi-14 for the use in nano imprint lithography [1, 2]. They concludedthat Si-14 functionalized with methacrylate as UV cross-linkable groupsshowed promising properties as planarizing layer on topology,patternable material and etch barrier. This is because of its properties(low viscosity 15 cP, low vapor pressure 0.8 Torr at 25° C., low UVshrinkage 5.0%, and with a high silicon content of 33%). However thesynthetic route for Si-14 requires many steps as shown in FIG. 2. Thereaction gave low yield (<20%) and took several days (>12 days) tosynthesize, therefore the route was not amendable to scaling to become acommercial product.

What is needed is a simpler synthesis that provides high yields in ashort amount of time, and results in useful compounds.

SUMMARY OF THE INVENTION

The present invention contemplates branched siloxanes (bothfunctionalized and unfunctionalized) as well as methods for making suchcompounds. In one embodiment, a method of synthesis is contemplatedcomprising reacting a siloxane which has silicon-hydrogen bondrepresented by the formula shown as (a) (where n represents a wholenumber between 1˜20) with an asymmetric linear siloxane represented bythe formula shown as (b) (where X represents any halogen and where mrepresents a whole number between 1 and 10, more preferably 2 and 10,and more commonly between 2 and 3) so as to generate a branched siloxanerepresented by the formula (c). This can be synthesized in a one stepreaction shown in FIG. 1, using asymmetric linear siloxanes asreactants. The route provides a shortened synthetic path, high yieldsand reduces the feed stock cost by 70% compared to the stepwise route.The synthesis is significantly lower in cost and easily scalable. Thebranched siloxane (c) can be further treated to attach additionalchemical moieties or functional groups as shown in FIG. 3.

In another embodiment, a method of synthesis is contemplated comprisingreacting a siloxane represented by the formula shown as (e) (where x andy independently represent a whole number between 1˜10) with anasymmetric linear siloxane represented by the formula shown as (b)(where X represents any halogen and where m represents a whole numberbetween 1 and 10, and more commonly between 2 and 3) so as to generate abranched siloxane represented by the formula (f) (see FIG. 4). Thebranched siloxane (f) can be further treated to attach chemical moietiesor functional groups such as that shown in FIG. 3 where X represents anybut not limited to moieties selected from the group consisting ofacrylates, methacrylates, vinyls, and epoxides.

The present invention contemplates, in one embodiment, a method forsynthesizing branched siloxanes, comprising, reacting i) a siloxanewhich has a silicon-hydrogen bond represented by the formula (a),wherein n represents a whole number between 1 and 20, with ii) anasymmetric linear siloxane of formula (b), wherein X represents anyhalogen and m represents a whole number between 2 or 3, said reactingperformed under conditions such that a branched siloxane and byproductsare produced. It is not intended that the present invention be limitedby the nature of the siloxane used as a reactant. In one embodiment,said asymmetric linear siloxane is made from a cyclic compound. In oneembodiment, said cyclic compound is hexamethylcyclotrisiloxane. In oneembodiment, said siloxane comprising a silicon-hydrogen bond representedby the formula (a) is 3H,5H-octamethyltetrasiloxane. In one embodiment,said 3H,5H-octamethyltetrasiloxane, prior to reacting with saidasymmetric linear siloxane, is exposed to a catalyst in the presence ofwater. In one embodiment, said catalyst is removed prior to reactingsaid 3H,5H-octamethyltetrasiloxane with said asymmetric linear siloxane.It is not intended that the present invention be limited to a particularcatalyst, however, a palladium catalyst is a preferred catalyst. It isnot intended that the present invention be limited to a particularhalogen. However, the preferred halogen of said asymmetric linearsiloxane is chlorine. In one embodiment, the present inventioncontemplates purifying the branched siloxane product free (orsubstantially free) of reactants and byproducts. In one embodiment, thepresent invention contemplates the further step of purifying thebranched siloxane by distillation, so as to remove said byproducts (orat least the majority of byproducts, and preferably at least 90% of saidbyproducts) of the synthesis reaction and provide a purified branchedsiloxane. In one embodiment, the present invention contemplates thefurther step of functionalizing said purified branched siloxane. In oneembodiment, said functionalizing comprises attaching chemical moieties;in a preferred embodiment, the chemical moieties are photo-crosslinkablemoieties, said moieties selected from the group consisting of acrylates,methacrylates, vinyls and epoxides. In one embodiment, saidfunctionalizing comprises hydrosilylation. The present invention alsocontemplates the compounds, as compositions of matter, described here,including but not limited to compounds made according to theabove-described methods. For example, the present invention contemplatesSi-12 having the structure shown in FIG. 10, as well as functionalizedSi-12 (FIG. 6), such as epoxy-Si-12 (FIG. 5).

The compounds have a variety of uses. One preferred, application is as anovel planarizing material for lithography, in which case functionalizedbranched siloxane, such as an epoxy-modified branched siloxane(epoxy-Si-12) is particularly useful. In one embodiment, the presentinvention contemplates spin coating formulations comprisingfunctionalized branched siloxanes onto patterned substrates. In oneembodiment, the present invention contemplates a planarizing layercomprising functionalized branched siloxanes made according to themethods of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the features and advantages of thepresent invention, reference is now made to the detailed description ofthe invention along with the accompanying figures.

FIG. 1 shows a reaction for the synthesis of branched siloxanes in a onestep reaction.

FIG. 2 shows a synthetic scheme for the synthesis of a branched siloxanematerial, Si-14, as previously reported in literature. This syntheticroute is stepwise and requires several iterations to extend the branchedsiloxane chain resulting in low yields and a time intensive process.

FIG. 3 shows a reaction of the current invention whereby branchedsiloxanes can be functionalized in a platinum catalyzed reaction. Thisprocess is referred to as a hydrosilylation.

FIG. 4 shows a reaction in which the starting siloxane is varied.

FIG. 5 shows the structure of a novel UV curable branched siloxane(epoxy-Si-12).

FIG. 6 shows the structure of functionalized UV curable branchedsiloxanes, in this case a functionalized-Si-12, wherein X represents achemical moiety, such as a photocurable and or a crosslinkablefunctional group.

FIG. 7 shows the mixture of epoxy Si-12 and PAG (photo acid generator)used in the formulation to spin coat a planarizing layer.

FIG. 8 shows the process flow, the formulation used, and the targetstack dimensions.

FIG. 9 shows the new synthetic route to obtain Si-12.

FIG. 10 shows the synthetic path to epoxy-Si-12.

FIG. 11 is a table of properties of epoxy-Si-12.

FIG. 12 shows the obtained spin-curve for the spin-coat study ofepoxy-Si-12.

FIG. 13 shows the optimized imprint dispense pattern.

FIG. 14 shows an SEM image of an imprint.

FIG. 15 shows an SEM image after planarization using epoxy-Si-12 wascarried out.

FIG. 16 shows the determined etch rate of epoxy-Si-12.

FIG. 17 shows the SEM image after the fluorine etch step.

FIG. 18 shows the desired pattern, indicating removal of the organicresist after O₂ etching (O₂: 3 sccm, Ar: 30 sccm, RF: 90 W, DC bias: 300V, pressure: 6 mTorr, Etching time: 8 minutes).

DEFINITIONS

To facilitate the understanding of this invention, a number of terms aredefined below. Terms defined herein have meanings as commonly understoodby a person of ordinary skill in the areas relevant to the presentinvention. Terms such as “a”, “an” and “the” are not intended to referto only a singular entity, but include the general class of which aspecific example may be used for illustration. The terminology herein isused to describe specific embodiments of the invention, but their usagedoes not delimit the invention, except as outlined in the claims.

A siloxane is any chemical compound composed of units of the form R₂SiO,where R represents an atom or a group of atoms including but not limitedto, a hydrogen atom, halogens, alkyl or aromatic groups. Siloxanes canhave branched or unbranched backbones consisting of alternating siliconand oxygen atoms —Si—O—Si—O—, with side chains R attached to the siliconatoms. These siloxanes can be “functionalized” by adding particularchemical moieties having desirable functional properties (as describedherein).

As used herein, “hydrogen” means —H; “hydroxy” means —OH; “oxo” means═O; “halo” means independently —F, —Cl, —Br or —I; “amino” means —NH₂(see below for definitions of groups containing the term amino, e.g.,alkylamino); “hydroxyamino” means —NHOH; “nitro” means —NO₂; imino means═NH (see below for definitions of groups containing the term imino,e.g., alkylamino); “cyano” means —CN; “azido” means —N₃; “mercapto”means —SH; “thio” means ═S; “sulfonamido” means —NHS(O)₂— (see below fordefinitions of groups containing the term sulfonamido, e.g.,alkylsulfonamido); “sulfonyl” means —S(O)₂— (see below for definitionsof groups containing the term sulfonyl, e.g., alkylsulfonyl); and“silyl” means —SiH₃ (see below for definitions of group(s) containingthe term silyl, e.g., alkylsilyl).

The term “alkylsilyl” when used without the “substituted” modifierrefers to a monovalent group, defined as —SiH₂R, —SiHRR′, or —SiRR′R″,in which R, R′ and R″ can be the same or different alkyl groups, or anycombination of two of R, R′ and R″ can be taken together to represent adialkyl substituent. The groups, —SiH₂CH₃, —SiH(CH₃)₂, —Si(CH₃)₃ and—Si(CH₃)₂C(CH₃)₃, are non-limiting examples of unsubstituted alkylsilylgroups. The term “substituted alkylsilyl” refers —SiH₂R, —SiHRR′, or—SiRR′R″, in which at least one of R, R′ and R″ is a substituted alkylor two of R, R′ and R″ can be taken together to represent a substituteddialkyl. When more than one of R, R′ and R″ is a substituted alkyl, theycan be the same of different. Any of R, R′ and R″ that are not eithersubstituted alkyl or substituted alkanediyl, can be either alkyl, eitherthe same or different, or can be taken together to represent a dialkylwith two or more saturated carbon atoms, at least two of which areattached to the silicon atom.

In addition, atoms making up the compounds of the present invention areintended to include all isotopic forms of such atoms. Isotopes, as usedherein, include those atoms having the same atomic number but differentmass numbers. By way of general example and without limitation, isotopesof hydrogen include deuterium and tritium, and isotopes of carboninclude ¹³C and ¹⁴C. Similarly, it is contemplated that one or morecarbon atom(s) of a compound of the present invention may be replaced bya silicon atom(s). Furthermore, it is contemplated that one or moreoxygen atom(s) of a compound of the present invention may be replaced bya sulfur or selenium atom(s).

Hexamethylcyclotrisiloxane is represented by the following structure:

3H,5H-octamethyltetrasiloxane is represented by the following structure:

Dimethylchlorosilane is represented by the following structure:

3-vinyl-7-oxabicyclo[4.1.0]heptane is represented by the followingstructure:

Bis(4-tert-butylphenyl)iodonium tris(trifluoromethylsulfonyl)methanideis represented by the following structure:

Photoacid generators (or PAGs) are typically cationic photoinitiators. Aphotoinitiator is a compound especially added to a formulation toconvert absorbed light energy, UV or visible light, into chemical energyin the form of initiating species, viz., free radicals or cations.Cationic photoinitiators are used extensively in optical lithography.The ability of some types of cationic photoinitiators to serve as latentphotochemical sources of very strong protonic or Lewis acids is thebasis for their use in photoimaging applications. The usualphoto-supplied catalyst has been strong acid. Triarylsulfonium anddiaryliodonium salts have become the standard PAG ingredients in achemically amplified resist formulations, because of their generallyeasy synthesis, thermal stability, high quantum yield for acid (and alsoradical) generation, and the strength and nonvolatility of the acidsthey supply. Simple onium salts are directly sensitive to DIN, X-ray andelectron radiations, and can be structurally tailored, or mixed withphotosensitizers, to also perform well at mid-UV and longer wavelengths.Nonionic PAGs such as phloroglucinyl and o,o-dinitrobenzyl sulfonates,benzylsulfones and some 1,1,1-trihalides are more compatible withhydrophobic media in general, although their thermal stabilities andquantum yields for acid generation are often lower.

It is not intended that the present invention be limited by the natureof the photoacid generator (PAG). There are several issues to beconsidered in the choice of the PAG, including but not limited tosufficient radiation sensitivity to ensure adequate strong acidgeneration for good resist sensitivity, absence of metallic elements,temperature stability, dissolution inhibition, etc. In one embodiment,triarylsulfonium (e.g. triphenylsulfonium nonaflate, ortri-p-hydroxyphenylsulfonium triflate) or diaryliodonium salts arepreferred because of their generally easy synthesis, thermal stability,high quantum yield for strong acid (and also radical) generation, andthe strength and nonvolatility of the acids they supply. It is also notintended that the present invention be limited by the developingsolvents used. In one embodiment, the developing solvent can be anaqueous solution of an alkali metal hydroxide, such as sodium hydroxideor tetramethylammonium hydroxide.

DETAILED DESCRIPTION OF THE INVENTION

One embodiment of the synthetic route contemplated by the presentinvention is illustrated in FIG. 1. A desirable branched siloxane (c) isobtained by using siloxanes having silicon-hydrogen bond represented as(a) and asymmetric linear siloxanes represented as (b). The asymmetriclinear siloxanes were prepared as described from a journal procedure inYoshino et al. 1990 [3] starting with, for example, commerciallyavailable cyclic compounds. The reaction conditions were optimized suchas determination of the amount of water and activated carbon needed. Forexample, one of the desirable linear siloxane (where m=2, X=Cl) wasobtained as a colorless liquid in 77.9% yield at 99.7% purity (GC/MS).

The reaction using the siloxanes having silicon-hydrogen bond andasymmetric linear siloxanes give not only the desirable branchedsiloxanes, but also undesired byproducts. The most effective method ofpurification of the product is distillation. Column chromatography isineffective to remove byproducts because they are also linear siloxanesthat show similar properties (polarities) with the desirable branchedsiloxanes. After distillation, the desirable branched siloxanes areobtained as colorless liquid. Nuclear Magnetic Spectroscopy (NMR), ¹H,¹³C and ²⁹Si, is useful to support the target structures. MatrixAssisted Laser Desorption Ionization (MALDI) spectroscopy (massspectroscopy) also verify the desirable mass numbers.

The new synthetic route to obtain Si-12 was successfully developed andis illustrated in FIG. 9. The optimized reaction to the final product,Si-12, took only two steps. This is a tremendous improvement in whichthe sought after product can be made in significantly higher yields andfewer steps compared to the previous synthetic route. The startingmaterials are relatively cheap and commercially available. The novelsynthetic route has also been shown to be easily scalable and thereforesuitable for industry.

Si-12 has two Si—H bonds, which can be converted to UV curable branchedsiloxanes. The synthetic path to epoxy-Si-12 is shown in FIG. 10. Thistype of reaction is referred to as a hydrosilylation. The reaction wassuccessfully carried out and product was recovered in high yields (87%).

The obtained branched siloxanes can be easily functionalized usingauthentic chemical reaction. For example, UV curable functional groupssuch as acrylates, methacrylates and epoxides can be introduced to thebranched siloxanes via the Si—H moiety. The reaction is referred to as ahydrosilylation reaction and is illustrated in FIG. 3 [4] where X is achemical moiety having desired functional properties. Hydrosilylation,also called catalytic hydrosilation, describes the addition of Si—Hbonds across unsaturated bonds. Ordinarily the reaction is conductedcatalytically and usually the substrates are unsaturated organiccompounds. Alkenes and alkynes give alkyl and vinyl silanes; aldehydesand ketones give silyl ethers. The functionalized branched siloxanes aretremendously useful in the semiconductor industry in processes includingplanarizing layers and patternable insulators.

Surface Hydrosilylation

The compounds described herein are useful for a variety of applications,including but not limited to, semiconductor fabrication. For example, asilicon wafer can be etched in hydrofluoric acid (HF) to remove thenative oxide, and form a hydrogen-terminated silicon surface. Then thehydrogen-terminated surfaces can react with unsaturated compounds (suchas terminal alkenes and alkynes), to form a stable monolayer on thesurface. The hydrosilylation reaction can be initiated with UV light atroom temperature, or with applied heat (typical reaction temperature120-200° C.), under moisture and oxygen free conditions. The resultingmonolayer is stable and inert, and prevents oxidation of the basesilicon layer. Surfaces of this kind could find applications in areassuch as molecular electronics, biochemistry, and direct electronicsensing of biomolecules.

In the present invention, it is possible to synthesize other branchedsiloxanes when starting siloxanes are changed to illustrated in (e),where x represents 1˜10, y represents 1˜10. The products are partiallybranched siloxanes shown in reaction shown in FIG. 4.

The compounds of the present invention can be used in layers as found inthe Ryuzaki et al U.S. patent application Ser. No. 11/571,017 [5],herein incorporated by reference.

The branched siloxanes can be functionalized with photo crosslinkablegroups such as acrylates, methacrylates, vinyls or epoxides etc. Thereactions are usually carried out through the Si—H bond of the branchedsiloxanes using a method called hydrosilylation.

In the following section, the present invention is described in muchmore detail. However, the present invention is not limited to thefollowing example. Hexamethylcyclotrisiloxane and dimethylchlorosilanewere purchased from Gelest Inc., USA. Activated carbon and Pt (dvs),Platinum(0)-1,3-divinyl-1,1,3,3-tetramethyldisiloxane complex solutionin xylene, Pt 2% were purchased from Aldrich, USA.3H,5H-Octamethyltetrasiloxane was purchased from Alfa Aesar, USA. Pd/C,Palladium on activated carbon (5% Pd) was purchased from Acros organic,USA. Allyl methacrylate was purchased from TCI, Japan.

DESCRIPTION OF PREFERRED EMBODIMENTS

In preferred embodiments, the invention is a synthesis for a novel UVcurable branched siloxane (epoxy-Si-12) illustrated in FIG. 5. From thepreviously synthesized Si-14 the siloxane chains were shortened becauseof the new synthetic route. Epoxide groups were selected to be used forcrosslinking. Functionalized Si-12 with epoxides showed a lower UVshrinkage than methacrylate based crosslinking. The synthesis wascarried out using conventional organic synthetic techniques. Thecharacterization of the materials were conducted by NMR (VARIAN 400MHz), GC/MS (Agilent Technologies 6890N attached with HP-5MS capillarycolumn, Agilent), CI-MASS (Dionex ultimate 3000) and MALDI-MASS (VARIANPro MALIDI 12 Tesla).

In further preferred embodiements the invention relates to the synthesisof other functionalized novel UV curable branched siloxanes(functionalized-Si-12) illustrated in FIG. 6, where in X represents aphotocurable functional group.

The properties of epoxy-Si-12 were investigated; appearance, ratio ofsilicon content, vapor pressure, viscosity, and shrinkage after the UVcure. The ratio of silicon content was calculated from the molecularweight of the monomer. The vapor pressure was measured by evacuating achamber containing epoxy-Si-12 submerged in liquid nitrogen. Then bysealing off the vacuum the pressure was measured after the epoxy-Si-12was thawed. The viscosity was measured by a Physica MCR 500 Rheometer.The UV shrinkage was calculated from the difference of film thickness onsubstrates by the use of an ellipsometer (J. A. Woollam) before andafter the UV cure.

Initially the spin coat study of epoxy-Si-12 was carried out on baresilicon wafers. Solvents such as PGMEA, PGME, cyclohexanone or butylalcohol, were not added into the formulation. Only 0.7 wt. % of PAG(photo acid generator), an example of which is illustrated in FIG. 7,was added to the epoxy-Si-12 to initiate crosslinking under the UVexposure. The spin rate of the substrates were set to 2500 rpm. In oneembodiment the photoacid generator is bis(4-tert-butylphenyl)iodoniumtris(trifluoromethylsulfonyl)methanide. The drop amount of epoxy-Si-12on 1 inch×1 inch silicon substrates was 200 μl. The film thickness afterUV exposure was measured by ellipsometry. All procedures were carriedout in a yellow room (UV cut-off filtered room).

The S-FIL/R demonstration using epoxy-Si-12 was carried out. The processflow, the formulation used, and the target stack dimensions can be seenin FIG. 8. The process consists of several steps; 1) substratepreparation, 2) imprint test features, 3) planarization usingepoxy-Si-12, 4) CHF₃ etch, 5) O₂ etch.

In the first step, the substrates were coated with an underlayer,NCI-NIL-01 (Nissan Chemical Industries, Ltd., Japan). The purposes ofsuch a material are to function as a transfer layer, improve adhesion,and a hard mask for a subsequent etch process to the silicon substrate.In the second step, imprints were carried out on a commercial imprinttool, Imprio 100 (Molecular Imprints Inc., USA) installed at theUniversity of Texas at Austin. A quartz template (mold) with 80 nm linesand 180 nm spaces was also purchased by the University of Texas atAustin. The template was pre-treated with a fluorinated surfacetreatment (Tridecafluoro-1,1,2,2-tetrahydro octyldimethylchlorosilanefrom Gelest Inc., USA) as a release layer before imprinting. In thethird step, CHF₃ etch was carried out on an Oxford Plasmalab 80 toremove excess epoxy-Si-12 layer. The etch ratio of epoxy-Si-12 wasdetermined to reach the correct etch depth. In the last step, O₂ etchwas carried out to break through the organic layer. SEM (Zeiss Neon 40)was used to measure stack thickness and etch depth after each stepexcept for the first.

The new synthetic route to obtain Si-12 was successfully developed andis illustrated in FIG. 9. The optimized reaction to the final product,Si-12, took only two steps. This is a tremendous improvement in whichthe desired product can be made in significantly higher yields and withfewer steps compared to previous synthetic routes. The startingmaterials are relatively cheap and commercially available. The novelsynthetic route has also been shown to be easily scalable.

Si-12 has two Si—H bonds, which can be converted to UV curable branchedsiloxanes. The synthetic path to epoxy-Si-12 is shown in FIG. 10. Thistype of reaction is referred to as a hydrosilylation. The reaction wassuccessfully carried out and product was recovered in high yields (87%).

Example 1 Synthesis of Asymmetric Linear Siloxane (b) (m=2, X=Cl)

A 2 L round bottomed glass flask equipped with a 250 ml addition funnelwas prepared. Hexamethylcyclotrisiloxane (116.7 g, 0.524 mol), activatedcarbon (2.151 g) and hexanes (330 ml) were added to the flask.Dimethylchlorosilane (88.5 ml, 0.795 mol) and hexanes (110 ml) wereadded to the addition funnel. The dimethylchlorosilane solution wasslowly added drop-wise over one hour under N₂ at room temperature. Thesolution was stirred vigorously overnight. The reaction was monitored byGC/MS periodically; if unreacted Hexamethylcyclotrisiloxane was stillpresent over 20%, additional activated carbon and dimethylchlorosilanewas added. The solution was filtered through 0.2 μm PTFE membrane toremove activated carbon. The solvent was removed under reduced pressureon a rotary-evaporator. Distillation under vacuum (below 10 Torr) at170° C. was carried out to purify the product. 129.6 g of the desirablecompound was obtained as a colorless liquid. CG/MS spectra showed 99.7%purity. The yield of reaction was 77.9%. ¹H NMR (CDCl₃): δ=4.69 (m, 1H),0.43 (s, 6H), 0.17 (d, J₂=2.80 Hz, 6H), 0.11 (s, 6H), 0.06 (s, 6H). ¹³CNMR (CDCl₃): δ=4.06, 0.88, 0.80, 0.68. ²⁹Si{¹H} NMR (CDCl₃): δ=3.75,−6.63, −18.94, −19.27. ²⁹Si NMR (CDCl₃): δ=3.75, −6.63 (J_(Si-H)=203.98Hz), −18.94, −19.27.

Example 2 Synthesis of Branched Siloxane (c) (n=2, m=3)

A 500 ml round bottomed glass flask equipped with a 100 ml additionfunnel was prepared. Pd/C (0.16 g), water (1.9 g, 0.106 mol) and THF(175 ml) were added to the flask. 3H,5H-octamethyltetrasiloxane (10.0 g,0.035 mol) and THF (75 ml) were added to the addition funnel. Thesolution was added slowly drop-wise into the flask and after completeaddition the reaction was stirred at room temperature for 6 hours. Thesolution was filtered through acid washed Celite™ to remove Pd/C. A 3 Lround bottomed glass flask with a 250 ml addition funnel was prepared.The previously synthesized asymmetric linear siloxane (b) (56.4 g, 0.178mol), triethylamine (27.8 g, 0.275 mol) and diethyl ether (700 ml) wereadded to the flask under positive N₂ pressure. The filtrate from theCelite™ filtration was added into the addition funnel and dropped slowlyinto the flask at 0° C. As soon as the addition was complete theice-bath was removed and the suspension was stirred overnight at roomtemperature. Water (1 L) was added to the solution to quench excessamounts of asymmetric linear siloxane before the aqueous and organiclayers were separated. The organic portion was washed three times withwater and dried over magnesium sulfate. The magnesium sulfate wasremoved by gravity filtration before the solution was reduced in vacuo.Distillation using a Kugelrohr apparatus at 170° C. and at 2 Torr wascarried out to remove byproducts as well as impurities. 28.9 g of acolorless liquid was obtained (93.1% yield). ¹H NMR (CDCl₃): δ=4.68 (m,2H), 0.17 (d, J=2.80 Hz, 12H) 0.08 (d, J=0.40 Hz, 18H), 0.07 (d, J=1.20Hz, 12H), 0.06 (s, 12H), 0.05 (s, 12H), 0.03 (s, 6H). ¹³C NMR (CDCl₃):δ=1.67, 1.04, 0.96, 0.85, 0.69, −2.27. ²⁹Si{¹H} NMR (CDCl₃): δ=7.70,−7.00, 19.95, −21.82, −22.08, −66.98. ²⁹Si NMR (CDCl₃): δ=7.70, −7.00(J_(SiH)=203.68 Hz), −19.94, −21.82, −22.08, −66.98. MALDI-MASS:m/z=897.235 (C₂₄H₇₄O₁₁Si₁₂Na⁺¹).

Example 3 Synthesis of Functionalized Branched Siloxane (d) (m=3, n=2,X=Methacrylate)

500 ml round bottle glass flask was prepared. The branched siloxane (c)(n=2, m=2) (12.0 g, 13.7 mmol), allyl methacrylate (4.41 g, 34.9 mmol))and toluene (130 ml) were added in the flask under N₂ atmosphere. 25drops of Pt(dvs) catalyst was added to the solution with vigorousstirring. The solution turned to a yellow color and stirring wascontinued overnight. The solvent was removed in vacuo. The excess allylmethacrylate was removed under vacuum (1 Torr) at room temperature. 14.9g of a slightly yellow liquid was obtained in 95.8% yield.

Example 4

The new synthetic route to obtain Si-12 was successfully developed andis illustrated in FIG. 9. The optimized reaction to the final product,Si-12, took only two steps. This is a tremendous improvement in whichthe sought after product can be made in significantly higher yields andfewer steps compared to the previous synthetic route. The startingmaterials are relatively cheap and commercially available. The novelsynthetic route has also been shown to be easily scalable and suitablefor industry.

Si-12 has two Si—H bonds, which can be converted to UV curable branchedsiloxanes. The synthetic path to epoxy-Si-12 is shown in FIG. 10. Thistype of reaction is referred to as a hydrosilylation. The reaction wassuccessfully carried out using the procedure described in Example 3 andthe product was recovered in high yields (87%).

Example 5 Properties of Epoxy-Si-12

The appearance of epoxy-Si-12 was a slightly yellowish liquid. It isspeculated that the reason for the color of the product is due to smallamounts of catalyst that were not removed completely in the purificationprocess. The material has a silicon content of 30.0%, which issufficiently high to withstand an O₂ etch process. The vapor pressure is0.65 Torr at 25° C. The viscosity is 29 cP at 25° C. Both of theproperties meet the requirements of an excellent planarizing material.The UV shrinkage was only 2.2%, which was lower than methacrylatederivatives (Si-14 was 5.1%). The all properties are summarized in FIG.11.

Example 6 Spin-Coat Study of Epoxy-Si-12

The obtained spin-curve is shown in FIG. 12. The result indicated thatapproximately 150 seconds of spin time is necessary to give a filmthickness in less than 1.0 μm. The data was useful for subsequentS-FIL/R demonstration.

Example 7 S-FIL/R Demonstration Using Epoxy-Si-12 Resist [6]

Step 1. NCI-NIL-01 (Nissan Chemical) was spin-coated to approximately100 nm thickness on bare silicon substrates as an underlayer.

Step 2. Imprints with an 80 nm lines and spaces template on an Imprio100® were carried out. One of the features of SFIL is an inkjet dispensesystem to dispense the liquid resist onto substrates. The optimizedimprint dispense pattern is illustrated in FIG. 13. The system wasdeveloped to take advantage of an authentic spin coat dispense system interms of not only residual layer uniformity but also to lower theconsumption of resist material. The optimized resist drop layout throughthe inkjet nozzle resulted in consistent and successful imprint pattern.

An SEM image of an imprint is shown in FIG. 14. The residual layer wasmeasured to approximately 52 nm, which is a little thicker than for thetraditional S-FIL process (less than 20 nm). Further optimization suchas lowering the resist volume or changing the imprint force, couldreduce the residual thickness. But in the case of the S-FIL/R process,it was acceptable because of the planarizing layer will coat and coverthe topography. The imprinted lines and spaces indicated values thatcorresponds to the features on the template.

Step 3. Planarization using epoxy-Si-12 was carried out and an SEM imageis shown in FIG. 15.

Step 4. The etch rate of epoxy-Si-12 was determined (CHF₃: 20 sccm, O₂:12 sccm, RF: 50W, DC bias: 192 V, Pressure: 30 mTorr) and is shown inFIG. 16. The actual etching of the planarizing layer was then carriedout.

FIG. 17 shows the SEM image after the fluorine etch step. Epoxy-Si-12was etched all the way to the top of the imprinted layer after. A totalof 10 minutes was required to reach such depth.

Step 5. O₂ etching was carried out to break through the organic layer(O₂: 3 sccm, Ar: 30 sccm, RF: 90 W, DC bias: 300 V, pressure: 6 mTorr,Etching time: 8 minutes). The result indicated that the organic resistwas removed and the desirable pattern was obtained as shown in FIG. 18.The width of lines and spaces was reversed compared to the initialimprint pattern, which indicates that reverse-tone S-FIL was achieved.

REFERENCES

-   1. Wei-Lun Jen, Frank Palmieri, Brook Chao, Michael Lin, Jianjun    Hao, Jordan Owens, Ken Sotoodeh, Robin Cheung, C. Grant Willson,    Proceeding of SPIE, 6517, (2007) 65170K-   2. Jianjun Hao, Michael W. Lin, Frank Palmieri, Yukio Nishimura,    Huang-Lin Chao, Michael D. Stewart, Austin Collins, Kane Jen, C.    Grant Wilson, Proceeding of SPIE, 6517, (2007) 651729-   3. Koji Yoshino, Akira Kawamata, Hiroaki Uchida, Yoshio Kabe,    Chemistry letters, pp. 2133, (1990)-   4. Chunxin Zhang, Richard M. Laine, J. Am. Chem. Soc. (2000) 122,    6979-6988)-   5. Ryuzaki, Daisuke and Fukuda, Hiroshi. Organic Siloxane Film,    Semiconductor Device Using the Same, Flat Panel Display Device, and    Raw Material Liquid. U.S. patent application Ser. No. 11/571,017    (published Dec. 18, 2008).-   6. S. V. Sreenivasan, D. Resnick, and C. G. Willson. “Using    reverse-tone bilayer etch in ultraviolet nanoimprint lithography”    Micromagazine, May, 2001.

1. A method for synthesizing branched siloxanes, comprising, reacting i)a siloxane which has a silicon-hydrogen bond represented by the formula(a),

wherein n represents a whole number between 1 and 20, with ii) anasymmetric linear siloxane of formula (b),

wherein X represents any halogen and m represents a whole number between2 to 10, said reacting performed under conditions such that a branchedsiloxane and byproducts are produced.
 2. The method of claim 1, whereinsaid siloxane comprising a silicon-hydrogen bond represented by theformula (a) is 3H,5H-octamethyltetrasiloxane.
 3. The method of claim 1,wherein m is either 2 or
 3. 4. The method of claim 2, wherein said3H,5H-octamethyltetrasiloxane, prior to reacting with said asymmetriclinear siloxane, is exposed to a catalyst in the presence of water. 5.The method of claim 4, wherein said catalyst is removed prior toreacting said 3H,5H-octamethyltetrasiloxane with said asymmetric linearsiloxane.
 6. The method of claim 4, wherein said catalyst is a palladiumcatalyst.
 7. The method of claim 1, wherein the halogen of saidasymmetric linear siloxane is chlorine.
 8. The method of claim 1,further comprising the step of purifying the branched siloxane bydistillation, so as to remove said, byproducts of the synthesis reactionand provide a purified branched siloxane.
 9. The method of claim 8,further comprising the step of functionalizing said purified branchedsiloxane.
 10. The method of claim 9, wherein said functionalizingcomprises attaching photocrosslinkable moieties, said moieties selectedfrom the group consisting of acrylates, methacrylates, vinyls andepoxides.
 11. The method of claim 9, wherein said functionalizingcomprises hydrosylilation. 12-14. (canceled)